A navigation system performs travel guidance for enabling a user to easily and quickly reach the selected destination. A typical example is a vehicle navigation system where a vehicle is provided with a navigation function to guide a user to a destination through a calculated route. Such a navigation system detects the position of the user's vehicle, and reads out map data pertaining to an area of the current user position from a data storage medium, for example, a CD-ROM (compact disc read-only memory), a DVD (digital versatile disc), or a hard disc. Typically, the navigation system displays a map image on a monitor screen while superimposing thereon a mark representing the current location of the user. At an intersection, the navigation system notifies the user which direction to turn at the intersection.
Such a navigation system is designed so that the user is able to scroll a map image to see other map image at a desired location and pin-point such a desired location. For example, a user scrolls the map image back and force to find a place such as a favorite restaurant in the city he/she is now visiting. The map scrolling operation may be performed by pointing a cursor on the screen and operating directional keys formed on the panel, remote controller, or touch-screen of the navigation system.
The map image on the navigation screen includes various map elements as well as marks used to identify types and/or names of business, etc. FIG. 1A shows an example of map image where only roads are illustrated whereas FIG. 1B shows an example of map image which includes numerous marks in addition to the roads on a screen 11. Typically, those marks are POI (point of interest) icons which are basically classified into generic POI icons and brand name icons.
In displaying the POI icons, on a map image on the screen, the navigation system may have to sacrifice its performance if the number of such POI icons to be displayed is too numerous. Moreover, too much icons on the map image on the screen can simply confuse the driver by hiding roads, intersections and other information. As shown in FIG. 1B, a map image is covered by a large number of brand name icons 75 and generic POI icons 73.
If a map image of a particular area having many generic POI icons 73 and brand name icons 75 is scrolled in a direction indicated by the cursor 18 as shown in FIG. 2A, too many icons are displayed, moved and overlapped as shown in FIG. 2B. This situation confuses the user because the map elements concerning more important information such as images of roads, directions of roads, and intersections become invisible. In many cases, too many icons on the screen other than the map elements and specific icons are not essential for user.
Further, since too many icons 73 and 75 are on the screen, the performance of the navigation system will be deteriorated, such as decrease of speed in the map scrolling operation, incorrect or incomplete map images, etc. This is because a large portion of the computing power of the navigation system must be used for displaying many icons while changing location of the map image. Accordingly, there is a need of new map scrolling method in which the navigation system selectively displays icons and map elements to assist the user in obtaining relevant information while achieving an optimum performance of the navigation system.